The present invention relates to a rolling bearing unit with a rotational speed sensor which rotatably supports a vehicle wheel of an automobile to a suspension and detects the rotational speed of the vehicle wheel so as to control the antilock brake system (ABS) and a traction control system (TCS).
Such a rolling bearing unit with a rotational speed sensor is disclosed for example in Japanese Utility Model First Publication No. H1-156464, and in French Patent First Publication No. 2732421.
FIGS. 6 and 7 shows a rolling bearing unit with a rotational speed sensor disclosed in French Patent First Publication No. 2732421. There is a first inner ring 1 which rotates with the vehicle wheel during use and called "hub". Formed on the outer peripheral surface at the axially outer end of the first inner ring 1 is a flange 2 with which the vehicle or road wheel is fixedly supported by the first inner ring 1.
Hereinafter, the term "axially outer" means the widthwise outer side when installed in the automobile, and left side in the drawings. On the contrary, the term "axially inner" means the widthwise central side when installed in the automobile, and right side in the drawings.
Formed on the outer peripheral surface at the axially middle portion of the first inner ring 1 is a first inner ring raceway 3, and formed on the outer peripheral surface at the axially inner end of the first inner ring 1 is a stepped portion 4 which is smaller in diameter than the first inner ring raceway 3.
Fitted on the stepped portion 4 is a second inner ring 6 on the outer peripheral surface of which a second inner ring raceway 5 is formed.
Provided around the first and second inner rings 1, 6 is an outer ring 7 which is not rotated during use.
Formed on the inner peripheral surface of the outer ring 7 are a first outer ring raceway 8 facing the first inner ring raceway 3 and a second outer ring raceway 9 facing the second inner ring raceway 5. In addition, formed on the outer peripheral surface of the outer ring 7 is a mount portion 10 which extends radially outward in a flange shape to mount the outer ring 7 to the suspension (not shown).
A plurality of rolling members 11a, 11b are provided between the first and second inner ring raceways 3, 5 and the first and second outer ring raceways 8, 9, respectively, so that the first and second inner rings 1, 6 are rotatably supported inside the outer ring 7. The rolling members 11a, 11b are rotatably held in a pair of cages 12.
Although balls are used for the rolling members in the examples illustrated, taper rollers can be used for the rolling members in the rolling bearing unit for a heavy automobile.
Provided between the cages 12 is a generally annular tone wheel 13 which is made of a magnetic material such as carbon steel and formed through a pressing process to have a larger cylindrical portion 14 with a larger diameter, a smaller cylindrical portion 15 with a smaller diameter and a connecting portion 16 to continuously and concentrically connect the larger cylindrical portion 14 and the smaller cylindrical portion 15 with each other.
Formed in the larger cylindrical portion 14 are a number of slit-like cutouts 17 which are arranged circumferentially with a uniform space therebetween and made axially long (left and right directions in the drawings). Accordingly, the magnetic property on the outer peripheral surface of the larger cylindrical portion 14 changes circumferentially alternately with a uniform interval.
The tone wheel 13 is mounted to the second inner ring 6 with the smaller cylindrical portion 15 fitted onto the outer peripheral surface at the axially outer end of the second inner ring 6 at a location spaced from the second inner ring raceway 5. In this state, the larger cylindrical portion 14 is located around the pair of cages 12.
On the other hand, formed in the axially middle portion of the outer ring 7 is a mount hole 18 which extends through the outer and inner peripheral surfaces of the outer ring 7 to insert the sensor 19 threrethrough. The sensor 19 has a detecting portion on its tip end face (lower end face in FIGS. 6 to 7).
In the state where the sensor 19 is fixedly inserted into the mount hole 18, the detecting portion faces through a clearance the outer peripheral surface of the larger cylindrical portion 14 of the tone wheel 13, so that when the first and second inner rings 1, 6 rotate, the output is changed corresponding to the change in magnetic property in the outer peripheral surface of the larger cylindrical portion 14.
When using the rolling bearing unit with the rotational speed sensor, the outer ring 7 is supported by the suspension while the vehicle wheel is fixed to the axially outer end of the first inner ring 1 at a location spaced from the outer ring 7 to support the vehicle wheel rotatably with reference to the suspension. When the tone wheel 13 rotates corresponding to the rotation of the vehicle wheel, the sensor 19 with its detecting portion facing the outer peripheral surface of the larger cylindrical portion 14 of the tone wheel 13 changes its output. The frequency at which the output of the sensor 19 changes is proportional to the rotational speed of the vehicle wheel. Accordingly, the output signal of the sensor 19 is sent through a harness 20 to the control devices to obtain the rotational speed of the vehicle wheel to properly control the ABS and the TCS.
In the conventional rolling bearing unit with the rotational speed sensor, it is difficult to secure the rigidity and simultaneously to make it compact and light weight. The reason is explained with reference to FIG. 2 showing an example of the embodiments of the present invention.
When using the rolling bearing unit to rotatably support the vehicle wheel, the moment load is applied to the first inner ring 1a in the direction to shift the central axis of the first and second inner rings 1a, 6a from the central axis of the outer ring 7a. The operating point of the moment load is located at the crossing point O between the central axis X of the first and second inner rings 1a, 6a and the extension line Y defining the contact angle .theta. associated with the axially inner rolling members 11b, the second inner ring raceway 5 and the second outer ring raceway 9. And, the moment load is applied to bend the first inner ring 1a based on the operating point at the crossing point O. This moment load is larger as the length L from the crossing point O is longer and equal to L.multidot.cos .theta..multidot.F, where .theta. is the contact angle and F is the force to press the rolling constant surface of the rolling member 11b to the second inner ring raceway 5.
Accordingly, it is desirable to make small the axial size of the first inner ring 1a (make the distance L small) or to make the cross sectional area of the first inner ring 1a larger as it is away from the crossing point O in order to prevent the first inner ring 1a from being bent regardless of the moment load.
However, in the conventional structure as shown in FIGS. 6, 7, since the tone wheel 13 is securely fitted onto the axially outer end of the second inner ring 6, the axial length of the second inner ring 6 and therefore the axial length of the stepped portion 4 for fitting with the second inner ring 6 are large. As clear in FIGS. 6 and 7, the cross sectional area of the stepped portion 4 is small, and therefore it is undesirable from the point of securing the rigidity of the rolling bearing unit to make the axial length of the stepped portion 4 longer.
The axial length of the second inner ring 6 and the axial length of the stepped portion 4 might be made shorter in the conventional structure of FIGS. 6 and 7, and the tone wheel 13 might be securely fitted onto the outer peripheral surface of the middle portion of the first inner ring 1. However, in this case, the tone wheel 13 would easily interfere with any one of the cages 12, so it would be hard to use the structure in practice.